1. Field of the Invention
The present invention relates to a feedhorn for a parabolic antenna used in a receiving unit of an antenna for receiving a satellite broadcast signal. More particularly, the invention relates to a feedhorn suitable to receive radio waves from a plurality of neighboring satellites.
2. Description of the Related Art
An example of a conventional feedhorn for receiving radio waves from a plurality of neighboring satellites will be described. Japanese Unexamined Patent Publication No. Hei 10-163737 discloses a feedhorn in which two waveguides are integrally formed and which can receive radio waves from neighboring two satellites.
In such a conventional feedhorn 23, as shown in FIGS. 12 and 13, first and second circular waveguides 21a and 21b each having a predetermined length and a diameter are formed. Around the first and second circular waveguides 21a and 21b, first and second grooves 22a and 22b each having a predetermined depth are formed by partition walls 22c, 22d, and 22e.
As shown in FIG. 13, the partition walls 22c, 22d, and 22e are formed so that their aperture end faces at the front end are flush with the same plane and their heights are the same.
A substrate 24 is disposed at the bottom of the first and second circular waveguides 21a and 21b. A feeding point 25 is provided so as to be positioned in the center of the bottom face of each of the circular waveguides 21a and 21b by printed wiring formed on the substrate 24. Further, a terminating unit 26 is attached to the bottom face of the feedhorn 23.
The conventional feedhorn 23 is attached to a receiving antenna and can receive radio waves transmitted from neighboring two broadcasting satellites by the first and second waveguides 21a and 21b.
A predetermined angle is, however, formed between the two neighboring broadcasting satellites to the feedhorn on the ground. Consequently, although either one of the aperture end faces formed on the same plane of the first and second circular waveguides 21a and 21b of the feedhorn can be adjusted at the predetermined angle formed by the neighboring two broadcasting satellites to the feedhorn, the other one cannot be adjusted. There is consequently a problem that radio waves from either one of the neighboring two broadcasting satellites cannot be properly received.
In order to solve the problem, it is possible to prepare two feedhorns (not shown) each having a single waveguide and attach the feedhorns to a receiving antenna so as to position each of the waveguides of the feedhorns at the angle formed by the neighboring two broadcasting satellites to feedhorn. There is, however, a problem such that assembly of the receiving antenna to which the feedhorns each having a single waveguide are separately attached is complicated and the cost is high.
The number of satellites recently launched is very large. A feedhorn provided with two waveguides can receive radio waves from only two satellites and has a problem that the feedhorn cannot receive radio waves from three or more satellites.